Go Back   IceInSpace > Equipment > Astrophotography and Imaging Equipment and Discussions

Reply
 
Thread Tools Rate Thread
  #1  
Old 26-03-2010, 06:27 AM
JohnH's Avatar
JohnH
Member # 159

JohnH is offline
 
Join Date: Feb 2005
Location: NSW
Posts: 1,179
Help please! Distorted Stars with Oiii filter

I have been attempting NB synthetic colour imaging

http://www.iceinspace.com.au/forum/showthread.php?t=58758

for the last week or so and I have hit a bit of a snag, well more than one as you can see, but I am looking for some ideas to help me track down why my Oiii frames show distorted stars.

Last night was clear again so I went back to NGC3372 see if I could get better Oiii data, before I did so I took my filter wheel apart, removed and cleaned the filters and re-assembled. As far as I can tell all the filters are screwed fully in (they were anyway), I also removed the filter holder and re-seated it.

However this did not improve things - my Ha frames show round stars but my Oiii images show a distortion in the star shapes - I am at a loss as to the cause of this? Is my filter faulty? I am beginning to think so as I have not seen this in LRGB frames.

Or could it be a focus issue - if I am not quite critically focussed the stars are better shapes but then I loose details, I can't really think it could be anything else as the only things changing are the filter and therefore the wavelength in the CCD light path.

Attached are a couple of raw light frames to show the issue, these are 4 min subs taken in sequence - and I have 32 of each showing the same issue...

Filters are the Astronomics ones
Filter wheel as an ATIK USB unit
Camera is an Opticstar 145M
Scope is a 127mm North Group APO (F7.5)
Image Scale is 1.4" / pixel





Attached Thumbnails
Click for full-size image (H_ngc3372_3.jpg)
120.9 KB36 views
Click for full-size image (O_ngc3372_3.jpg)
153.6 KB36 views
Reply With Quote
  #2  
Old 26-03-2010, 01:19 PM
JohnH's Avatar
JohnH
Member # 159

JohnH is offline
 
Join Date: Feb 2005
Location: NSW
Posts: 1,179
Processed result

Here is how the procssed image looks
Attached Thumbnails
Click for full-size image (etasmall.jpg)
192.3 KB18 views
Reply With Quote
  #3  
Old 26-03-2010, 01:27 PM
multiweb's Avatar
multiweb (Marc)
ze frogginator

multiweb is offline
 
Join Date: Oct 2007
Location: Hinchinbrook
Posts: 18,220
Could it be a slight tilt? The elongation seems uniform across the whole field. Have you tried to rotate the Oiii filter 90 degrees in its cell then shoot again? That should tell you if it's a problem within the filter holder frame or glass, or the filter wheel?
Reply With Quote
Reply

Bookmarks

Thread Tools
Rate This Thread
Rate This Thread:

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump


All times are GMT +10. The time is now 04:48 PM.

Powered by vBulletin Version 3.8.7 | Copyright ©2000 - 2019, Jelsoft Enterprises Ltd.
Advertisement
OzScopes Authorised Dealer
Advertisement
Meade Australia
Advertisement
Celestron Australia
Advertisement
NexDome Observatories
Advertisement
Bintel
Advertisement
Lunatico Astronomical
Advertisement
SkyWatcher Australia
Advertisement
Astronomy and Electronics Centre
Advertisement